Active warming of saline or blood is ineffective when standard infusion tubing is used: an experimental study

To determine the effect of infusion rate, tubing length and fluid composition on the temperature of the infusate reaching the distal end of an infusion tubing with and without active fluid warming.

Warmed normal saline (W-NS) and packed red blood cells (W-PRBC), were infused with a fluid warmer through a modified infusion set. The fluids were delivered at eight infusion rates from 50 to 999 mL x hr(-1). The infusate temperature was monitored at 20 cm intervals on the iv tubing. The same temperature monitoring protocol was applied to PRBC without warmer (NoW-PRBC).

In W-NS and W-PRBC groups, there was a decrease in the infusate temperature, at each flow rate, from the drip chamber to the distal end of tubing ( P <0.001). In NoW-PRBC group, there was a rapid increase in the infusate temperature from the bag to the drip chamber ( P <0.001). Thereafter, there was no change in temperature, except at the 999 mL x hr(-1) infusion rate, where a slight increase in the infusate temperature throughout the tubing was shown. In W-NS and W-PRBC groups increasing the flow rate produced a significant increase in the infusate temperature, at each measurement point ( P <0.001). In the NoW-PRBC group, increasing the flow rate did not alter the infusate temperature. The fluid composition did not influence the infusate temperature.

There is an important heat exchange within the tubing, which is aggravated at low flow rates. At infusion rates appropriate for pediatric anesthesia the clinical and economic value of fluid warming without the use of heated extension tubing is questionable.